Ignition timing control system for internal combustion engine

ABSTRACT

An ignition timing control system for an internal combustion engine comprising a circuit for generating a reference ignition signal in synchronism with the engine, a circuit for generating a retard ignition signal at a point shifted by a selected shaft angle of the engine from the reference ignition signal, and an ignition circuit for controlling the ignition timing of the engine according to the retard ignition signal. The retard ignition signal generator includes a capacitor circuit for charging and discharging, a first constant-current circuit for always supplying a first current to the capacitor circuit, a second constant-current circuit for supplying a second current larger than the first current to said capacitor circuit, a switching circuit which starts the flow of the second current in synchronism with the reference ignition signal and cuts off the second current when the terminal voltage across said capacitor circuit reaches a reference level, and an output circuit for generating a retard ignition signal in synchronism with the cutting-off operation of said switching circuit.

This invention relates generally to an ignition timing control systemfor an internal combustion engine and, more particularly concerns anignition timing control system in which a retard ignition signal isgenerated.

In general, an ignition timing control system for an internal combustionengine is arranged so as to provide spark at a point shifted by acertain retard position from an advance position where the engineprovides the maximum output power, in order to reduce the amount ofharmful ingredient (nitrogen oxides NOx) contained in the exhaust gas toprevent vehicle air pollution. To this end monostable multivibratorshave been used in the past to generate a retard ignition signal. Forexample, in the Japanese Patent Post-Exam. Publication No. 46012/74(which was filed on Sept. 28, 1970 and published on Dec. 7, 1974), thereis disclosed a constant-current circuit which acts to charge a capacitorfor providing a non-stable time to a mono-stable multivibrator and aconstant-current circuit which functions to discharge the capacitor,these two circuits being co-operatively connected so that the capacitorcharges and discharges alternately thus to generate an ignition signalas soon as the non-stable time period of the mono-stable multivibratorhas elapsed. The elapsed or retard time is proportional to the ignitionperiod of the engine, as long as the capacitor maintains its constantcharge and discharge currents accurately. That is, the retard time willproduce an ignition signal shifted by a retard angle of a predeterminedshaft angle of the engine.

In the system of the type referred to, since the capacitor for charge ordischarge is connected at the high-level side of a transistor whichforms the multivibrator, and the two constant-current circuits for thecapacitor are disposed at the high-level side of the capacitor; thecharging and discharging range of the capacitor will become narrow. As aresult, it is impossible to control the retard ignition time of theengine accurately over a wide range from the low speed to a high speedand to provide stable constant-current circuits. In addition, due to thefact that the multivibrator produces a negative potential at thebase-side terminal connected to the capacitor, it is impossible for thesystem to be employed as an integrated circuit.

Assume now that the period of an ignition signal supplied to the engineis T, the non-stable time for the mono-stable multivibrator is α, thedischarging current for the capacitor is I₁, and the charging current isI₂. Since the charge (T-t₁)I₂ accumulated in the capacitor duringcharging is equal to the energy t₁ I₁ drained during discharging, theretard time for the ignition signal or non-stable time α is expressed asfollows. ##EQU1## The expression means that the ignition period isproportional to the engine speed. Further, consider N (r.p.m) to be thenumber of revolutions of the engine, and ω(rad/sec) to be an angularvelocity. Accordingly, an angle θ the engine rotates during a time `t`is written as follows. ##EQU2## From the above expressions (1) and (2),it follows that a retard angle ##EQU3## Since, 6NT is be an angle whichcorresponds to an ignition period, from expression (2); 6NT is found tobe a constant of 90 degrees for a 4 cylinder engine distributor and of60 degrees for a 6 cylinder engine distributor. As a result, retardangle θα is proportional to I₂ /(I₁ +I₂).

When the retard angle θα is controlled by adjusting parameter I₁ or I₂to obtain a desired engine speed or load or an engine temperature,however, one of the difficulties with the above-mentioned system is thatsince α does not vary linearly with I₁ or I₂, it is impossible tocontrol the engine in a suitable manner.

Furthermore, in a conventional system, a reference ignition signal insynchronism with the rotation of the distributor is shaped into a squarewave pulse, the trailing edge of the pulse is used as a referenceignition timing, and at this point, a retard ignition signal generatorwill generate a retard ignition pulse. In a non-contact igniting system,an output transistor in an ignition circuit is made conductive justbefore ignition, and thus turning the output transistor off will startthe ignition immediately. In this case, in order to delay the ignitiontiming, cancelling of the reference ignition signal with the retardignition signal before the trailing edge of the reference ignitionsignal operates the output transistor will provide the delay onlybetween the generation of the reference ignition signal to the output ofthe retard ignition signal at the time of cutting off the outputtransistor. For this reason, such a system has a defect in that too longa time is required for generating the retard ignition signal which willcause the reference ignition signal to act first to the output signal,which results in undesired ignition prior to the desired retardignition.

Via one or more transistors, the reference ignition signal is suppliedinto the retard ignition signal generator and sent from the retardignition signal generator to the reference ignition controlling circuit.However, in order to generate a retard ignition signal in the retardignition signal generator, the generator requires more transistors thanthe above-mentioned ones. This means that the retard ignition signal isdelayed through the operation lag of so many transistors and thus afterthe reference ignition signal, arrives at the output terminal of theretard ignition signal generator. Particularly, in the case that theretard ignition signal generator is replaced with an integrated circuitin which capacitors, diodes or resistors are formed by transistors inorder to minimize the generator, the transfer speed difference betweenthe reference ignition signal and the retard ignition signal will beincreased remarkably, causing the above-mentioned faulty operation ofthe system.

There is also well known a system in which according to the operationconditions, either the reference or retard ignition signal is selectedto operate the ignition circuit. For example, a system of this kind isdisclosed in the above-mentioned Japanese Post-Exam Publication No.46012/74. However, in this conventional system, as soon as ignitioncontrol is switched from the control by the reference ignition signal tothe control by the retard ignition signal, the charge alreadyaccumulated in the capacitor may often generate an undesired ignitionsignal, which may lead to incorrect ignition timing. Particularly,ignition at a point shifted by an advance angle from the maximum advanceangle may cause a serious damage of the engine.

Accordingly, it is an object of the present invention to provide animproved ignition timing control system for an internal combustionengine which generates a retard ignition signal with an accurate retardangle with respect to the reference ignition signal.

It is a further object of the present invention to provide an ignitiontiming control system of the above kind for an internal combustionengine in which the retard angle in the retard ignition signal withrespect to the reference ignition signal varies directly with anexternal control signal.

It is a further object of the present invention to provide an ignitiontiming control system of the kind for an internal combustion enginewhich prevents incorrect ignition due to the reference ignition signalwhen a retard ignition signal controls the ignition timing of theengine.

It is yet another object of the invention to provide an ignition timingcontrol system for an internal combustion engine which avoids incorrectignition directly after the switching in the case that either thereference ignition signal or the retard ignition signal is selectivelyused.

The above and other objects and advantages of the present invention willbecome clear from the following description with reference to theaccompanying drawings, in which:

FIG. 1 is a circuit diagram of an embodiment of an ignition timingcontrol system for an internal combustion engine according to thepresent invention;

FIG. 2 is a timing diagram showing the operational waveforms of themajor part of the ignition timing control system of FIG. 1;

FIGS. 3A, 3B and 4 are waveforms and the characteristic of an outputtransistor in an ignition circuit of the ignition timing control systemaccording to the present invention;

FIG. 5 is a circuit diagram of an embodiment of a current limit timereducing circuit in the system of FIG. 1;

FIG. 6 is a timing diagram showing the operational waveforms of themajor part of the current limit time reducing circuit of FIG. 5;

FIG. 7 is a timing diagram showing the operational waveforms of themajor part of a retard ignition signal generator in the system of FIG.1;

FIG. 8 is a timing diagram showing the operational waveforms used forcontrol of the ignition timing according to the present embodiment;

FIG. 9 is an ignition timing control characteristic of the presentembodiment;

FIG. 10 is a circuit diagram of an embodiment of a switching circuit inthe system of FIG. 1; and

FIG. 11 is a circuit diagram of another embodiment which controls thecharging current for the capacitor.

Now, the present invention will be explained with reference to preferredembodiments in conjunction with accompanying drawings.

Turning now to the drawings, there is shown in FIG. 1 an ignition timingcontrol system which includes a retard ignition signal generator. Areference ignition controlling circuit A consists of sections 1 to 5 anda retard ignition signal generator B consists of sections 7 to 11. 1 isa reference ignition signal generator, and 2 is a signal amplifier forshaping a signal from the reference ignition signal generator 1. Thesignal shaped in the amplifier 2 is applied to an ignition circuit 3.When the ignition circuit 3 receives the signal, it acts to cut off theprimary current through an ignition coil C, thereby to cause the highvoltage induced in the secondary winding of the ignition coil C to sparkin ignition plug G. A current limiting circuit 4 is provided to limitthe current in the primary winding of the ignition coil C in order topermit the flow of enough secondary current to ignite the ignition plugG. A current limit time reducing circuit 5 is activated in response tothe activation of the current limiting circuit 4, and functions to theduty of a signal from the signal generator 1 so as to minimize the timerequired to limit the current.

The retard ignition signal generator B receives the reference ignitionsignal and produces a retard ignition signal to provide to the ignitioncircuit. As has been explained above, the retard ignition signalgenerator B consists of sections 7 to 11. 7 is a trigger signalgenerator which receives the reference ignition signal and generates atrigger signal. 8 is a bistable multivibrator which is driven in onestate in response to a trigger signal from the trigger signal generator7. A triangular pulse forming circuit 9 is provided to form a triangularpulse through a constant-current charge/dicharge circuit which includesa capacitor Q. An output circuit 10 including a comparator CMP isprovided to detect the discharging voltage across the capacitor circuitQ and as soon as the discharging voltage drops to a predetermined value,invert the bistable multivibrator 8 to supply a retard ignition signalto the ignition circuit 3. A switching circuit 11 for connecting ordisconnecting the retard ignition signal generator B to the referenceignition circuit A functions to connect that trigger signal sent intothe bistable multivibrator 8 to the earthed line when the retardignition signal is unnecessary, and to pass the charge accumulated inthe capacitor Q to the earth line.

In FIG. 1, the circuit encircled with a chain-dotted line and generallydesignated MIC is formed with a single chip of a monolithic intergratedcircuit (MIC). The chip MIC is mounted on a printed circuit board (inwhich resistors are already printed) along with a capacitor chip whichis not contained in the chip MIC. The printed circuit board mounted withthe chips is then jointed by means of suitable adhesive on a coolingbody (which functions to radiate heat) on which a power transistor chipis already mounted, so that the elements on the printed circuit boardand the power transistor chip on the cooling body are electricallyinter-connected to form an ignition circuit module.

The operation of the ignition timing control system for an internalcombustion engine according to the present invention will now bedetailed in the following.

Referring first to the reference ignition signal generator 1 in theillustrated embodiment, a pick-up coil 100 is provided which isinterlinked to the closed magnetic path formed in the distributor.

The shaft of the distributor rotates in synchronism with the rotation ofthe engine. The distributor is arranged so that while the distributorshaft rotates one turn, that is, the engine crank shaft rotates twoturns, the magnetic flux through the closed magnetic path varies by thesame turns as the number of the engine cylinders. As such magnetic fluxvaries, an alternating current such as shown in FIG. 2, (a) appearsacross the pick-up coil 100.

One terminal of the pick-up coil 100 is connected via a resistor 101 tothe positive terminal of a battery and via a forwardly connected diode102 to the common line (earth), respectively. The diode 102 is used forcompensating the temperature in a transistor T₁. A reverse connecteddiode 103 with respect to the battery is connected across the diode 102to bias the reverse voltage applied across the diode 102. The otherterminal of the pick-up coil is connected resistors 104 and 105 to thebase of the transistor T₁. Between the resistors 104 and 105, isconnected a capacitor 106 for suppressing noise. On the other hand,across the resistor 105, is connected a capacitor 107 which acts to passa switching signal from the pick-up coil 100 through the capacitor 107to the transistor T₁.

The forward voltage drop across the diode 102 is designed so as to beslightly high with respect to the potential drop between the base andemitter of the transistor T₁. Therefore, a current flows through thebase and emitter of the transistor T₁, resistor 101, the pick-up coil100 and resistors 104 and 105 until the base of the transistor T₁ isbiased in the reverse direction, which maintains the transistor T₁ inthe ON (conductive) mode.

The collector and emitter of the transistor T₁ are respectively via aresistor 109 and a resistor 110 to the positive terminal of the batteryand the common line. A diode 108 is reversely connected between the baseof the transistor T₁ and the common line to avoid the application of thereverse voltage between the base and emitter thereof.

The operation of the reference ignition signal generator 1 arranged inthis manner will be now explained.

When the voltage is induced in the pick-up coil 100 with the positivepolarity at the terminal thereof connected to the diode 102 and drops toa point `b` in FIG. 2 (a), the transistor T₁ is increasingly biased inthe reverse direction thus to turn the transistor T₁ off. The inducedvoltage in the pick-up coil 100 further increases in the negativedirection and as soon as it reaches a point `c`, the polarity of theinduced voltage abruptly reverses with the positive polarity at theterminal of the coil connected to the resistor 104. When the voltagearrives at a point `d` in the course of the reversing, the transistor T₁is again put at operative level, which cause the transistor T₁ to turnon. It will be appreciated from the foregoings that while the voltageacross the pick-up coil is between a point `b` and a point `d`, thetransistor T₁ is off, while, the voltage is between a point `d` and apoint `b'` in the next waveform, the transistor is on. The transistionof the transistor T₁ is shown as function with respect to the collectorpotential thereof in FIG. 2 (b).

Since the reference ignition signal generator 1 is arranged so thatturning the transistor T₁ off will turn on the power transistor in theignition circuit 3, as long as the transistor T₁ is off, that is, thevoltage across the pick-up coil 100 is at a point between the points `b`and `d`, the power transistor remains on. As soon as the coil voltagereaches the point `d`, the transistor T₁ is turned on and on thecontrary, the power transistor is turned off. At the same time, theprimary current in the ignition coil is cut off to induce an ignitionvoltage in the secondary winding thereof.

Turning next to the amplifier 2 for amplifying the reference ignitionsignal, it is provided with a transistor T₂ the base of which isconnected through a resistor 201 to the collector of the transistor T₁.The emitters of the transistors T₁ and T₂ is directly connected and thenconnected through an emitter resistor 110 to a common line. Thetransistors T₁ and T₂ form a Schmitt circuit. The collector of thetransistor T₂ is connected via a resistor 202 to the positive terminalof the battery.

The base, collector and emitter of an amplifying transistor T₃ areconnected respectively, to the collector electrode of the transistor T₂,to the positive terminal of the battery via a resistor 203, and directlyto the common line. The collector of the transistor T₃ is connected viaa line l₁ to the retard ignition signal generator B to pass thereference ignition signal. The collector is also connected through aforward connected diode 204 to the base of a transistor T₄.

On the other hand, the collector of the transistor T₄ is connectedthrough a resistor 205 to the positive terminal of the battery and theemitter thereof is directly to the common line. A capacitor 206 isprovided between the base and emitter of the transistor T₄. Thecapacitor 206 is formed between the P and N layers of the monolithic ICand the electrostatic capacity thereof is on the order of 30 picofarads.The capacitor 206 and the diode 204 form a Miller integrator andfunctions to delay the turn-off time of the transistor T₄ bymicroseconds.

The collector of the transistor T₄ is coupled to the base of atransistor T₅. The collector and emitter of the transistor T₅ arerespectively to the positive terminal of the battery via a resistor 207and to the common line via a resistor 208. The emitter of the transistorT₅ is directly coupled to the base of a transistor T₆. The collector andemitter of the transistor T₆ are respectively connected to the positiveterminal of the battery via an external resistor 209 and directly to thecommon line. The interconnection between the base of the transistor T₅and the retard ignition signal generator B is established by means of asignal input line l₂, the interconnection between the base of thetransistor T₆ and the current limit time reducing circuit 5 isestablished by means of a signal input line l₃.

The above-mentioned amplifier 2 operates as follows.

Since while the transistor T₁ is on, the collector of the transistor T₁has an identical potential with the emitter of the transistor T₂, thetransistor T₂ remains off without flowing a current between the base andemitter thereof. As soon as the output voltage from the pick-up coil 100causes the transistor T₁ to be cut off, the collector potential of thetransistor T₁ increases to conduct current between the base and emitterof the transistor T₂, turning the transistor T₂ on. Since thetransistors T₁ and T₂ form a Schmitt circuit, such operation is carriedout in a very short time. The on state of the transistor T₂ continuesuntil the transistor T₁ is turned on by the output signal from thepick-up coil, that is, the reference ignition signal generates. Thestate of the operation in the transistor T₂ is shown as a function withrespect to the collector potential thereof in FIG. 2 (c).

The operational signal shown in FIG. 2 (c) is further inverted andamplified through the transistor T₃. The inverted and amplified signalis sent via the diode 204 to the transistor T₄ and at the same time viathe line l₁ to the retard ignition signal generator B. This operation isillustrated as a function with respect to the collector potential of thetransistor T₃ in FIG. 2 (d). When the transistor T₃ is turned off andthe collector thereof becomes high level, a current flows between thebase and emitter of the transistor T₄ via the diode 204, thereby to turnthe transistor T₄ on. In this case, the current through the diode 204charges the biasing capacitor 206 with the polarity shown in FIG. 1. Forthis reason, even if the transistor T₃ is turned on thus to drop thecollector potential thereof to the common line potential, while thecharge accumulated in the capacitor 206 is discharged through the baseand emitter of the transistor T₄, the transistor T₄ maintains on. Thismeans that the transistor T₄ will not be turned off immediately. Thisoperation is illustrated as a function with respect to the collectorpotential of the transistor T₃ and the collector potential with respectto the transistor T₄ in FIG. 2 (d) and (e), respectively. The transistorT₄ is cut off time τ₁ later after the transistor T₃ is switched from theoff mode to the on mode. τ₁ is on the order of microseconds.

Turning the transistor T₄ off will conduct current through the resistor205, the base and emitter of the transistor T₅ and then the resistor208, which causes the transistor T₅ to be turned on. This operationalstate is shown as a function with respect to the collector potential ofthe transistor T₅ in FIG. 2 (f). Current through the collector andemitter of the transistor T₅ and the resistor 208 is partly directed tothe base and emitter of the transistor T₆. Turning the transistor T₅ onwill turn the transistor T₆ on immediately. As a result, current flowingso far through the resistors 209 and 210 to the ignition circuit 3 asthe post stage will start flowing through the collector and emitter ofthe transistor T₆ to the common line, resulting in the cutting off ofthe power transistor in the ignition circuit. Therefore, the ignition bymeans of the reference ignition signal without a retard ignition signalwill be actually achieved time T₁ later after the pick-up coil voltagereaches a point `d` in FIG. 2 (a).

On the other hand, where the retard ignition signal generator B isoperatively coupled to the reference ignition controlling circuit A, ifthe reference ignition signal is supplied to the retard ignition signalgenerator B via the line l₁ simultaneously when the transistor T₃ isturned off, a retard ignition signal is applied from the generator B tothe base of the transistor T₅ via the line l₂. In this case, the retardignition signal has a time width T₃ and is issued which lags from thereference ignition signal by time T₂ as illustrated in FIG. 2 (g). Tothis end, the cut-off lag time T₁ of the transistor T₄ through theMiller integrator is selected to be greater than the retard time T₂after the transistor T₃ is turned on before the retard ignition signalis applied to the base of the transistor T₅. The retard ignition signalacts to lower the base potential of the transistor T₅ to the common linepotential. For this reason, turning the transistor T₄ off will notincrease the base potential of the transistor T₅ immediately and willmaintain it at the common line potential as far as the trailing edge ofthe retard ignition signal. As a result, in the case the retard ignitionsignal is issued, the power transistor in the ignition circuit 3 isturned off the time (τ₂ +τ₃) later, that is, the time after thetransistor T₃ is turned on before arriving at the trailing edge of theretard ignition signal. The ignition will be delayed θ₁ =(τ₂ +τ₃ -τ₁) ascompared with the ignition by means of the reference ignition signal.This operation is given as a function with respect to the collectorpotential of the power transistor circuit when the ignition circuitoperates, and of the collector potential thereof when a retard ignitionsignal activates the ignition circuit, in FIGS. 2 (h) and (i),respectively.

Turning next to the ignition circuit 3, a power transistor circuitconsisting of two transistors T₇ and T₈ is contained. The twotransistors T₇ and T₈ are interconnected to form a Darlingtonconnection. The base of the transistor T₇ is connected via a resistor210 to the collector of the transistor T₆, the collector thereof isdirectly connected to the collector of the transistor T₈, and theemitter thereof is directly to the base of the transistor T₈. Thecollector of the transistor T₈ is connected via a primary winding C₁ ofan ignition coil C to the positive terminal of the battery, and theemitter thereof is connected via a register 301 to the common line. Inaddition, between the collector and the common line, is provided a diode305 in the reverse direction. Between the base and emitter of thetransistor T₇ and between the base and emitter of the transistor T₈,respectively, are provided resistors 302 and 303. Between the collectorand base of the transistor T₈, is placed a Zener diode 304, with theanode at the collector and the cathode at the base.

The ignition circuit 3 operates as follows.

When the transistor T₆ is turned on in response to the referenceignition signal or a retard ignition signal, current flowing so farthrough the resistors 209 and 210 to the base of the transistor T₇ willstop, which results in the turning off of the transistor T₇. At the sametime, the transistor T₈ is also turned off in which current has beenflowing through the collector and emitter of the transistor T₇ into thebase of the transistor T₈. This interrupts the current flowing so farthrough the collector and emitter of the transistor T₈ into the primarywinding C₁ of the ignition coil C, thus inducing a high voltage on thesecondary winding C₂ of the ignition coil C. This high voltage is due tothe flyback voltage in the ignition coil C.

The operation explained above will be described according to FIG. 3A andFIG. 3B which are waveforms as a function of the primary winding currentI_(c) with respct to time and of the collector potential V_(CE) of thetransistor T₈ with respect to time, respectively. When the primarywinding current is cut off at time t_(o), the current decreases with aconstant gradient along points `a`, `b` and `c` on the turn-offcharacteristic, as shown in FIG. 3A. In this case, as soon as theprimary winding current is turned off, the collector potential of thetransistor T₈ will abruptly increase from point `a` to the breakovervoltage V_(z) of the Zener diode 304, as shown in FIG. 3B. Since thebreakover voltage of the Zener diode 304 is set so as to be lower thanthat between the collector and emitter of the transistor T₇ or T₈, priorto the transistors T₇ and T₈, the Zener diode 304 will breakover wherebythe Zener current i_(z) flowing through the Zener diode starts to flowthrough the base and emitter of the tarnsistor T₈. As a result, thecollector current i_(c) will flow through the collector of thetransistor T₈.

The collector current i_(c) is expressed as follows in terms of theZener current i_(z) through the base and the current amplificationfactor h_(fe8) of the transistor T₈.

    i.sub.c =h.sub.fe8 ·i.sub.zc

The collector current i_(c) acts to suppress the increase of theimpedance between the collector and emitter of the transistor T₈ tomaintain the collector potential at the breakover voltage V_(z). Thecurrent i_(z) is approximately 10 milliamperes and the currentamplification factor h_(fe8) is approximately 50, so that the collectorcurrent is approximately 500 milliamperes. The collector current i_(c)causes the potential of the transistor T₈ to be lowered, as seen best atpoint `b` in FIG. 3B. However, the small collector current will notcause the Zener diode 304 to cut off and the primary winding currentitself is lowered adequatedly, whereby the Zener diode will not be cutoff until the transistor T₈ has a less collector potential than theZener voltage. In this way, the collector potential of the transistor T₈is cramped due to the breakover voltage V_(z) of the Zener diode 304, asseen best at point `c` in FIG. 3B.

When the primary winding current further decreases to reach point `c` inFIG. 3A, the collector potential becomes lower than the breakovervoltage V_(z) of the Zener diode 304, thereby to cut off the Zener diode304, as shown at point `c` in FIG. 3 (b). As will be understood frompoints `c`, `d` and `e` in FIGS. 3A and 3B, after that, although thecollector potential decreases as the current decreases, even after thecurrent becomes zero the collector potential does not settle down atzero immediately and decays gradually as oscillating to zero. Suchdamping will occur in tens microseconds after the primary windingcurrent is cut off. There is shown in FIG. 4 a characteristic as afunction of the primary winding current I_(c) with respect to thecollector potential of the transistor T₈. In FIG. 4, the parts alreadydescribed with reference to FIGS. 3A and 3B are denoted by the samesymbols and variation directions as in FIGS. 3A and 3B.

In case that incorrect ignition provides a reverse application of thehigh voltage across the secondary winding of the ignition coil tobetween the emitter and collector of the transistor T₈, the diode 305acts to protect the transistor T₈ against such a high voltage by biasingthe high voltage. The two transistor T₇ and T₈ in Darlington connection(which has been already explained earlier) and the Zener diode 304 maybe formed as a single semiconductor chip, for example, such as disclosedin the Japanese Laid-open Publication No. 27277/77 in which two P layersfor transistors and one P layer for a Zener diode are incorporated in acommon N layer.

There is shown in FIG. 1 the current limiting circuit 4 which includesresistors 401 and 402 in series which are connected across the resistor301. A connection between the resistors 401 and 402 leads to the base ofa transistor T₉. The collector and emitter of the transistor T₉ arerespectively to the collector of the transistor T₆ and to the commonline. The operation and configuration of such a current limiting circuitis well known. For example, one such current limiting circuit isdisclosed in the U.S. Pat. No. 3,605,713.

The operation of the current limiting circuit 4 used in the illustratedembodiment will be explained in the following.

When the transistor T₆ is turned off to turn the power transistor on,the primary winding current will increase not in the step form but inthe gradually increasing form due to the reactance of the primarywinding, as seen best in FIG. 2 (j). The voltage drop across theresistor 301 increases linearly with the primary winding current. Assoon as the primary winding current reaches approximately 6 amperes, thevoltage drop across the resistor 301 becomes a predetermined value,which provides a potential enough to turn the transistor T₉ to theconnection between the resistors 401 and 402. Turning the transistor T₉on will cause part of the current so far supplied into the base of thepower transistor to be directed to the common line via the collector andemitter of the transistor T₉. This decreases the base current of thepower transistor, so that increase of the primary winding current stops,resulting in a constant current of 6 amperes of the primary windingcurrent. In other words, in order to keep the primary winding currentunder a predetermined limit, the base current of the power transistor isrestricted to increase the impedance between the collector and emitterof the power transistor thereby to suppress the increase of the primarywinding current. That is, the current supplied from the battery will notexceed 6 amperes. In the illustrated embodiment, it has been found that6 amperes of the primary winding current will produce spark voltagesuitable for ignition of the ignition plugs, in various operation modesof the engine.

In FIG. 2 (j), broken lines indicate the primary current cutting timingdue to a reference ignition signal, and solid lines indicate that due toa retard ignition signal.

Turning next to the current limit time reducing circuit 5, the circuit 5is connected through a line l₄ to the collector of the transistor T₈ sothat the circuit 5 detects potential variation in the collector of thetransistor T₈ via the line l₄ and as soon as the collector potentialreaches the predetermined limit, it varies the bias potential to shortenthe turn-off time of the transistor T₁.

FIG. 5 shows a circuit diagram of an embodiment of the current limittime reducing circuit 5. In the figure, an avalanche diode 501 isinserted in the line l₄. The avalanche diode 501 is directly to thecollector of a transistor T₁₀. The base and emitter of the transistorT₁₀ are connected respectively to the emitter of the transistor T₅ via aresistor 502 and a line l₃, and to the common line. Resistors 503 and504 in series are placed between the collector and emitter of thetransistor T₁₀, a connection between the resistors 503 and 504 leads tothe base of a transistor T₁₁ via a diode 505. The collectors of thetransistors T₁₀ and T₁₁ is connected to the positive terminal of thebattery via resistors 506 and 507, respectively. The collector of thetransistor T₁₁ is further connected to the base of a transistor T₁₂ viaa capacitor 508, a diode 509 and a resistor 510. The emitter of thetransistor T₁₁ is connected directly to the common line. A connectionbetween the capacitor 508 and the diode 509 leads to the common line viaa diode 511 and a resistor 512, as shown in FIG. 5. On the other hand, aconnection between the resistor 510 and the cathode electrode of thediode 509 leads to the common line via a capacitor 513. The collectorand emitter of the transistor T₁₂ are connected respectively to thepositive terminal of the battery, and to the base of the transistor 1via a line l₅ which includes a resistor 514.

The circuit of an embodiment of the current limit time reducing circuitoperates as follows.

After the power transistor is turned on, if the current limiting circuit4 provides a limitation of the collector current of the power transistorto increase the collector potential thereof, then the avalanche diode501 will break over thus to increase the potential at the connectionbetween the resistors 506 and 503. Since the transistor T₆ is off aslong as the power transistor is on, the transistor T₁₀ is also off. As aresult, variation in the collector potential of the power transistorwill directly appear at the connection between the above-mentionedresistors 506 and 503. The collector potential of the power transistordue to the current limitation abruptly varies in an extremely short timeas in increase of the collector potential at the time that the primarywinding current is cut off, so that potential variation at theconnection between the resistors 506 and 503 will also occur in the samemanner. The increment at the connection potential is divided by theresistors 503 and 504, and the voltage drop across the resistor 504 isapplied to the transistor T₁₁ via the diode 505, thereby to turn thetransistor T₁₁ on. This operation continues until the power transistoris turned off. That is, as soon as the transistor T₅ is turned on inorder to turn the power transistor off, current flows through the baseof the transistor T₁₀ via the resistor 502, turning the transistor T₁₀on. As a result, the potential at the connection between the resistors506 and 503 drops to the common line level, resulting in turning off ofthe transistor T₁₁. This means that the transistor T₁₁ remains on onlyduring the time period δ₁ (see FIG. 6 (a)) the power transistor is putunder the current limitation state.

Turning the transistor T₁₁ on will cause the charge accumulated so farin the capacitor 508 to be discharged through the collector and emitterof the transistor T₁₁. In this case, since the time constant for thecapacitor 508 upon the discharging is a constant value and determined bythe capacitor 508 and the resistor 512, the discharged amount is roughlyproportional to the turnon time of the transistor T₁₁, that is, thecurrent limit time. The discharging state is shown in FIG. 6 (b) withdecreasing portion of the waveform. A longer current limit time δ₁ willprovide an increase of the charge amount to be discharged from thecapacitor 508, so that the remaining charge amount is decreasedcorrespondingly to turn off the transistor T₁₁, whereby it takes alonger time Δ to charge the capacitor 508 through the current flowingthe resistor 507, the capacitor 508, the diode 509 and the capacitor513. As a result, the charging voltage across the capacitor 513 rises asseen in FIG. 6 (c) to increase the conductivity of the transistor T₁₂thereby to supply much current to the base of the transistor T₁ via theline l₅. At this point, the cut-off bias level at the base of thetransistor T₁ drops from level k₁ to level k₂, as seen best in FIG. 6(d). For this reason, the time interval the transistor T₁ remains onwill be decreased from time p₁ to time p₂. This results in reduction ofthe time interval that the power transistor keeps on, whereby thecurrent limit time is shortened from δ₁ to δ₂, as shown in FIG. 6 (a).

When a retard ignition signal is used to control the ignition timing,the power transistor is put conductive during much longer than the casewhere a reference ignition signal is used, resulting in a longer currentlimit time. However, the current limit time reducing circuit 5 acts toreduce the turn-off time of the transistor T₁ to a suitable level, as inthe above-mentioned manner.

Next, explanation will be made with reference to the parts 7 to 11 inthe retard ignition signal generator B.

There is first shown the trigger signal generator 7 in which a referenceignition signal is supplied from the line l₁ which, in turn, leads tothe collector of the transistor T₃.

The reference ignition signal is applied to the base of a transistor T₁₃via a resistor 701.

The emitter and collector of the transistor T₁₃ are connectedrespectively to the common line, and to the base of a transistor T₁₄ viaa forward connected diode 702. Similarly, the emitter and collector ofthe transistor T₁₄ are connected respectively to the common line, and tothe cathode of a diode 703. The collectors of the transistors T₁₃ andT₁₄ are also connected to the collector of a transistor 801 withmultiple collector terminals. The anode of the diode 703 is connected tothe anodes of two diode 704 and 705, the cathode of the diode 704 isconnected to the collector of the transistor T₁₃, and the cathode of thediode 705 is connected to the bistable multi-vibrator 8. In addition,between the base and collector of the transistor T₁₄, is provided acapacitor 706 which consists of a capacitance of 10 to 30 picofaradsprovided between the P and N layers in the monolithic integratedcircuit. The capacitor 706 and the diode 702 form a Miller Integrator.

The operation of the trigger signal generator 7 will be explained withreference to FIG. 7.

When the pick-up voltage shown in FIG. 7 (a) varies to provide the baseof the transistor T₁ to a cut-off level, the transistor T₁ will beturned off and at the same time, the transistor T₃ will be turned off,as seen in FIG. 7 (b). Turning the transistor T₃ off will pass currentby way of the line l₁ from the positive terminal of the battery to thebase and emitter of the transistor T₁₃, which causes the transistor T₁₃to be turned on. This operation is shown in FIG. 7 (c) as a functionwith respect to the collector potential of the transistor T₁₃. Turningthe transistor T₁₃ on will stop abruptly the base current of thetransistor T₁₄ through the diode 702, thus turning the transistor T₁₄off. The charge accumulated so far in the capacitor 706 will startflowing through the base of the transistor T₁₄, whereby the transistorT₁₄ changes with a slight lag time from the on mode to the off mode (seeFIG. 7 (d)).

Then, when the pick-up voltage varies as far as point `d` to turn on thetransistor T₃, the transistor T₁₃ is turned off to pass current throughthe base of the transistor T₁₄ and the diode 702, thereby turning thetransistor T₁₄ on.

However, during a very short period the capacitor 706 is charged asshown in the figure, the transistor T₁₄ will be turned on with a slightdelay, as seen best in FIG. 7 (d). During the delay time interval t_(a),current will not pass through either the diode 703 or 704, as will beunderstood from FIG. 7 (e). As a result, during the delay time t_(a),current flows through the diode 705 to the bistable multivibrator 8, andis used as a trigger signal shown in FIG. 7 (e).

There is shown a bistable multivibrator 8 which basically consists oftwo transistors T₁₅ and T₁₆ which have operating characteristics reverseto each other. The emitter, collector and base of the transistor T₁₅ areconnected respectively to the common line, to one of the collectors ofthe transistor 801 via a resistor 802, and to the collector of thetransistor T₁₆ via a reverse connected diode 803. Likewise, the emitter,collector and base of the transistor T₁₆ are connected respectively tothe common line, to one of the collectors of the transistor 801 and tothe collector of the transistor T₁₅ via a resistor 804. Further, thediode 705 has the cathode connected to the base of the transistor T₁₅.

The operation of the bistable multivibrator 8 will now be explained.

Applying a trigger signal to the base of the transistor T₁₅ via thediode 705 will turn the transistor T₁₅ on. As soon as the transistor T₁₅is turned on, the collector potential thereof drops to the common linelevel, whereby the base potential of the transistor T₁₆ becomes at thecommon line level so that the transistor T₁₆ is turned off. Turning thetransistor T₁₆ off will increase the collector potential thereof, sothat current continues to flow through the diode 803 to the base of thetransistor T₁₅ whereby the transistor T₁₅ is put under the on mode.

Since the multi-collector transistor 801 has multiple collectors withrespect to a pair of the emitter and base and the base-emitter currentis shared with respect to all collectors, currents through thecollectors are all the same. In other words, the transistor 801 isconfigurated as a current mirror circuit.

Referring to the triangular pulse forming circuit 9, the circuit 9 isprovided with a transistor T₁₇ the base of which is connected to thecollector of the transistor T₁₅ in the bistable multivibrator 8. Inaddition, the triangular pulse forming circuit 9 is provided with adischarging/charging capacitor circuit Q which includes two capacitors901 and 902 in series. The capacitor circuit Q is charged or dischargedthrough a constant-current by means of a constant-current chargingcircuit and a constant-current discharging circuit.

A transistor T₁₈ forms an element of the constant-current dischargingcircuit. The collector and emitter of the transistor T₁₈ are connectedto the capacitor circuit Q and to the common line, respectively. Thebase of the transistor T₁₈ is connected both to the common line via theemitter and collector of the transistor T₁₇, and to a constant-voltagecircuit for providing a constant voltage to the base of the transistorT₁₈.

Where the bistable multivibrator 8 produces no output, that is, thetransistor T₁₅ has a high voltage at the collector thereof; thetransistor T₁₇ is in the on mode, the base of the transistor T₁₈ is atthe common line level, and thus the transistor T₁₈ remains off. In thiscase, the capacitor circuit Q is charged through the externalconstant-current charging circuit. Transistors T₁₉ and T₂₀ form theabove-mentioned constant-current charging circuit which acts to chargethe capacitor circuit Q through a constant-current. The transistor T₁₉has two colletors, that is, is of a multi-collector type, and forms acurrent mirror circuit with transistor T₂₀. One of the two collectors ofthe transistor T₁₉ is coupled to the capacitor circuit Q, and the otheris coupled to the common line via the collector and emitter of thetransistor T₂₀. The emitter and base of the transistor T₁₉ charge withthe two collectors so that the two collectors have an identical current.On the other hand, the base of the transistor T₂₀ is connected to theconstant-voltage circuit to supply a constant voltage to the same base,so that the collector-emitter current in the transistor T₂₀ is constant.This means that a constant current flows through the capacitor circuit Qwhich leads to the collector of the transistor T₁₉, and thereby tocharge the capacitor circuit Q through the constant current.

The emitter of the transistor T₁₉ is coupled both to the positiveterminal of the battery via the external resistor 90, and to the cathodeof the Zener diode 905 the anode of which leads to the common line. Theswitch SW is arranged so that a resistor can be switched either to theanode of the Zener diode 906 or to an external terminal h₀. From theterminal h₀, is supplied a control signal which depends on the speed andload of the engine. With the switch SW switched in the illustratedposition, the Zener diode 906 has the resistor 907 and the diode 908connected in series therewith. The diode 908 has the cathode connectedto the common line. A connection between the resistor 907 and the diode908 is coupled to the base of the transistor T₂₀. Further, the Zenerdiode 906 has resistors 909 and 910 and a diode 911 (the cathode ofwhich leads to the common line) in series therewith, and a connectionbetween the resistor 910 and the diode 911 is coupled to the base of thetransistor T₁₈.

A connection between the resistors 909 and 910 is coupled via a resistor912 to the collector of a transistor T₂₂ the emitter of which, in turn,is coupled to a diode 913. The diode 913 has the cathode connected tothe common line. On the other hand, a connection between the capacitors901 and 902 is coupled to the collector of a transistor T₂₁ the emitterof which, in turn, is directly coupled to the common line. The bases ofthe transistors T₂₁ and T₂₂ are coupled to external signal terminals h₁and h₂ on the MIC (which has been already explained earlier).

The base circuit of the transistor T₁₈ has a constant potential by meansof the Zener diode 906, that is, a constant potential determined by theforward voltage drop of the diode 911. The transistor T₁₈ and the basecircuit thereof form a current mirror type of the constant currentcircuit, so that the current I₁ through the collector and emitter of thetransistor T₁₈ is equal to that through the base circuit thereof whichincludes the resistors 909 and 910.

In the similar way to the base circuit of the transistor T₁₈, the basecircuit of the transistor T₂₀ has a constant potential by means of theZener diode 906, that is, a constant potential determined by the forwardvoltage drop of the 908. The transistor T₂₀ and the base circuit thereofform a current mirror type of the constant-current circuit, so that thecurrent I₂ through the collector and emitter of the transistor T₂₀ isequal to that through the base circuit thereof which includes theresistor 907.

As has been explained above, the transistor T₁₉ is of a multi-collectortype. Therefore, the emitter-base current of the transistor T₁₉ isshared with the respective collectors thereof so that currents throughthe collectors are all the same. This means that the current I₂ throughthe collector and emitter of the transistor T₂₀ is equal to that throughthe two collectors of the transistor T₁₉.

The transistor T₂₁ is provided to connect the capacitors 901 and 902 inseries, or to disconnect the capacitor 902. Input of a signal into theexternal signal terminal h₁ will cause the transistor T₂₁ to be turnedon to short-circuit the capacitor 902, so that the charging current I₂flows only through the capacitor 901. The capacity of the capacitor 901is selected to be about 20 times that of the capacitor 902. For thisreason, when an signal is applied to the external signal terminal h₁,the capacity of the capacitor circuit Q substantially consists of thatof that capacitor 901 with a larger capacity, whereas, when no signal isapplied to the terminal h₁, the capacitor circuit Q substantiallyconsists of the capacitor 902 with a smaller capacity. The signal at theterminal h₁ is provided at the time of starting the engine, and acts toeliminate the deterioration of the charging characteristic due to thefact that the power source voltage is low and the ignition period islong during the starting of the engine.

On the other hand, input of a signal into the external signal terminalh₂ will cause the transistor T₂₂ to be turned on, which passes a partcurrent I₃ out of the current through the resistor 909 into thecollector and emitter of the transistor T₂₂. This decreases the current(I₁ -I₃) through the resistor 910 so that the base current of thetransistor T₁₈ decreases. Therefore, the charging current I₁ for thecapacitor circuit Q decreases from I₁ to (I₁ -I₃) so that it takes alonger time to discharge capacitor circuit Q until the dischargedvoltage reaches a predetermined level. A signal is also provided at theterminal h₂ during starting the engine, and avoids the reduction of thedischarging time due to the decreased charging voltage when a signal isapplied to the terminal h₁.

Now, the operation of the triangular pulse forming circuit 9 will bedescribed in the following.

As soon as a signal from the trigger circuit 7 turns on the transistorT₁₅ in the bistable multivibrator 8, the base potential of thetransistor T₁₇ drops, whereby the transistor T₁₇ is turned off. Thetransistor T₁₈ the base of which has been kept at the common line leveldue to the transistor T₁₇, will be then turned on, which forms aconstant-current discharging circuit of the capacitor circuit Q. Throughthe transistor T₁₈, flows a total current I₁ of the constant-current I₂for charging of the capacitor circuit Q and the discharging currentI_(Q). When the transistor T₂₂ is on, the current I₁ is expressed asfollows. ##EQU4##

Where, V₉₀₆ is the breakover voltage for the Zener diode 906, V₉₁₁ isthe forward voltage drop of the diode 911, R₉₀₉ is the value of theresistor 909, and R₉₁₀ is the value of the resistor 910.

As soon as the terminal voltage across the capacitor circuit Q arrivesat the reference voltage V_(ref) during discharging, the output circuit10 at the latter stage will operate to invert the bistable multivibrator8, so that the transistor T₁₅ has a high level at the collector thereof.This will again cause the transistor T₁₇ to be turned on to drop thebase potential of the transistor T₁₈, thus turning the transistor T₁₈off. As a result, the discharging of the capacitor circuit Q stops. Atthe same time, the capacitor circuit Q begins charging through theconstant current I₂ which is supplied from the transistor T₁₉.

The constant current I₂ is given as follows. ##EQU5##

Where, V₉₀₉ indicates the breakover voltage of the Zener diode 906, V₉₀₈is the forward voltage drop of the diode 908, and R₉₀₇ is the value ofthe resistor 907.

In this way, since the capacitor circuit Q is charged and dischargedthrough the constant currents I₁ and I₂, the terminal voltage appears asa triangular waveform (or saw-tooth) pulse with constant gradients `m`and `n`, as seen in FIG. 7 (g). In the illustrated embodiment, thedischarging current I₁ is about 100 milliamperes and the chargingcurrent I₂ is about 5 milliamperes.

Turning the transistor T₂₂ on will pass into the diode 913 the partialcurrent I₃ of the base current through the transistor T₁₈ whichdetermines the discharging current. The shunt ratio of the base currentof the transistor T₁₈ to the part current I₃ is set to be on the orderof 1:0.5 to 1:3. At the same time, the cathode areas of the diodes 911and 913 is selected so that the densities of the currents through thediodes 911 and 913 are essentially the same. This is helpful in matchingboth the forward temperature characteristics of the diodes 911 and 913through which a large current flows as compared with the chargingcurrent.

The non-common-line terminal of the capacitor circuit Q is connected tothe anode of a diode 903 the cathode of which, in turn, is connected viathe resistor 90 to the positive bus of the battery. With a power switchK at the closed position, the diode 903 has a high level at the cathodethereof, thus passing no current through the diode 903. When the powerswitch K is switched to the open position, the power bus voltage dropsto the common line level, whereby the change accumulated in thecapacitor circuit Q is moved to the common line via the diode 903 andthe resistor 90. Then, the power switch K is turned on, the terminalvoltage across the capacitor circuit Q becomes zero.

There is shown in FIG. 1 the output circuit 10 which has resistors 121and 122 and a comparator CMP. The resistors 121 and 122 are connected inseries combination, across the Zener diode 906 in the triangular pulseforming circuit 9 so as to produce the reference voltage V_(ref). Thenon-grounded terminal of the resistor 122 is coupled to the negativeinput terminal of the comparator CMP, and the non-grounded terminal ofthe capacitor circuit is coupled to the positive input terminal of thecomparator CMP. The output terminal 124 of the comparator CMP is coupledboth to the collector of the transistor T₁₆ in the bistablemultivibrator 8, and to the base of a transistor T₂₃ via a resistor 123.The emitter and collector of the transistor T₂₃ are coupled to thecommon line and to the collector of the transistor T₄ in the amplifiercircuit 2 via the line l₂ , individually.

The output circuit 10 operates as follows.

When the capacitor circuit Q in the triangular pulse forming circuit 9discharges to reach the reference voltage V_(ref) at the negativeterminal of the comparator CMP, the last stage transistor (not shown) inthe comparator CMP is turned on to provide the common line level to theoutput terminal 124 of the comparator. Accordingly, the base potentialof the transistor T₁₅ drops through the diode 803, thereby turning offthe transistor T₁₅. Turning the transistor T₁₅ off will increase thecollector potential thereof to provide current to the base of thetransistor T₁₆. This will turn the transistor T₁₆ on, and thereby toinvert the bistable multivibrator. In this case, the base current of thetransistor T₁₇ in the triangular pulse forming circuit 9 begins flowing,thereby causing the transistor T₁₇ to be turned on. Turning thetransistor T₁₇ on will provide the common line level to the base of thetransistor T₁₈, so that the transistor T₁₈ is turned off thus to stopdischarging the capacitor circuit Q. As a result, the charging of thecapacitor circuit Q starts again through the constant current I₂ togenerate the next reference ignition signal, and continues until atrigger signal from the trigger circuit 7 causes the bistablemultivibrator to be inverted.

There is shown in FIG. 7 (f) the inverting operation of the bistablemultivibrator 8 as a function with respect to the collector potential ofthe transistor T₁₆, in which the discharging time interval of thecapacitor circuit Q corresponds to the inverse time interval τ₃ of thebistable multivibrator, as will be seen as a matter of course.

On the other hand, the output of the comparator CMP will drop the basepotential of the transistor T₂₃ to the common line level, therebyturning off the transistor T₂₃. This will pass the current flowingthrough the line l₂ to the base of the transistor T₅ so that thetransistor T₅ is turned on to cut off the power transistor in theignition circuit 3, thereby cutting off the primary current in theignition coil. The above-mentioned operations are shown in FIGS. 2 (g),(i) and (j). It will be seen from FIG. 2 (j) that the primary windingcurrent on the ignition coil C is cut off at a time shifted by retardangle θ₁ with respect to the reference ignition time (indicated by abroken line).

As will be seen from FIG. 7 (h), when the discharging voltage of thecapacitor circuit reaches V_(ref), the output from the comparator CMPdrops to the common line level instantaneously. At the output time, thecollector potential of the transistor T₂₃ changes from the common linelevel to a high level (see FIG. 7 (i)) and at the same time, the primarywinding current I_(c) is cut off (see FIG. 7 (j)).

Referring now to the switching circuit 11, there is provided atransistor T₂₄ the collector of which leads to one of the collectors ofthe multi-collector transistor 801. The emitter of the transistor T₂₄ isconnected to the common line. The base of the transistor T₂₄ isconnected both to a diode 311 the anode of which leads to the commonline, and to the positive terminal of the battery via an externalresistor 91 and a switch S. In addition, the collector of the transistorT₂₄ is connected both to the base of a transistor T₂₅ via a resistor312, and to the base of a transistor T₂₆ via a resistor 313. Thecollector and emitter of the transistor T₂₅ are connected to the base ofthe transistor T₁₅ in the bistable multivibrator 8 and to the commonline, respectively.

On the other hand, the collector and emitter of the transistor T₂₆ aredirectly connected to the base of the transistor T₁₇ in the triangularpulse forming circuit 9, and to the common line, respectively.

The operation of the switching circuit 11 will be explained in thefollowing.

When the power switch K is turned on, current flows through the resistor90 and the Zener diodes 905 and 906, whereby different voltages appearacross the Zener diodes 905 and 906. This will activate theconstant-current charge/discharge circuit in the triangular pulseforming circuit 9, the output circuit 10, the bistable multivibrator 8and the trigger circuit 7. Therefore, this would supply a retardignition signal from the retard ignition signal generator B to thereference signal ignition controlling circuit A as long as the powerswitch K is at the on position.

For this reason, the switch S is turned off to stop the retard ignitionsignal. Turning the switch S off will turn the transistor T₂₄ off toincrease the collector potential thereof. This will pass current throughthe emitter and collector of the transistor 801 and the resistors 312and 313 to the bases of the transistors T₂₅ and T₂₆, causing thetransistors T₂₅ and T₂₆ to be turned on. Turning on the transistor T₂₅will connect a trigger signal to the common line via the diode 705 ofthe trigger circuit 7 and the collector and emitter of the transistorT₂₅, which makes it impossible to invert the bistable multivibrator 8.

As has been already described above, as soon as the power switch K isturned off, the charge accumulated in the capacitor circuit Q willdischarge through the diode 903. Accordingly, immediately after thepower switch K is turned on, the terminal voltage across the capacitorcircuit Q will be lower than the reference voltage V_(ref) from thecomparator CMP. This means that the voltage at the output terminal 124of the comparator CMP drops to the common line level and the transistorT₁₅ in the bistable multivibrator 8 has a low potential at the basethereof, with the transistor T₁₅ is in the off mode. Thus, just afterthe power switch K is turned on, the transistor T₁₅ will be off and thetransistor T₁₆ will be on, in the bistable multivibrator 8. For thisreason, under a condition where it is impossible to invert the bistablemultivibrator 8 as has been described above, the transistor T₁₇connected at the base thereof to the collector of the transistor T₁₅will be on, the transistor T₁₈ will be off, and the discharging circuitfor the capacitor circuit Q will be cut off. On the other hand, the openposition of the switch S means that the transistor T₂₆ is on, and thusthe base of the transistor T₁₇ drops to the common line level throughthe transistor T₂₆, so that even if the transistor T₁₅ in the bistablemultivibrator 8 is in the off mode, the transistor T₁₇ will not beturned on. As a result, the transistor T₁₈ is turned on to form thedischarging circuit for the capacitor circuit Q. The charging current I₂through the capacitor circuit Q also flows through the transistor T₁₈,and thereby to maintain the terminal voltage across the capacitorcircuit at the common line level. With the terminal voltage across thecapacitor circuit Q at the common line level, since the output of thecomparator CMP is also at the common line level, the transistor T₂₃ willremain of and the output line l₂ will is always at the same level as thecollector potential of the transistor T₄.

In this way, as long as the switch S is off, the trigger signal will notissue a retard ignition signal from the output circuit.

The switch S may be replaced with an electronic switch such as atransistor, in addition to a mechanical switch. Further, the switch Smay be used with not only a single switch but also a logical operationcircuit of two or more switches. Depending on the type of the usedengine, conditions required for the retard iginition signal might bedifferent between one another. In either case, if only the switch Scircuit is replaced with one which has operating characteristicssuitable for the conditions required by the engine, the other parts ofthe system according to the present invention can be used.

Here is an embodiment of the switch circuit.

There is shown in FIG. 10 a switch circuit S (which is encircled by abroken line) in which the reference ignition controlling circuit Abetween the positive terminal of the battery and the common line. Inaddition, between the positive terminal and the common line, areprovided a resistor 51 and Zener diodes 52 and 53 in series. The diodes52 and 53 are both have anodes connected to the common line. Aconnection between the Zener diodes 52 and 53 is connected to the baseof a transistor T₂₇. The collector and emitter of the transistor T₂₇ arecoupled to the positive terminal of the battery and to the common linevia the resistor 91 and the diode 311, respectively. Furthermore, thebase of the transistor T₂₇ is coupled to the positive terminal of thebattery via a water temperature switch 54 and a resistor 55. The watertemperature switch 54 functions to turn on or off according to thetemperature of cooling water for the engine, that is, it is turned offwhen the cooling water temperature is below 50° C. and turned on whenthe temperature exceeds 50° C. The Zener diodes 52 and 53 are set so asto break over as soon as the power voltage exceeds 9 volts the switchcircuit S operates as follows. In case that the water temperatureexceeds 50° C. or the power voltage exceeds 9 volts, the transistor T₂₇will be turned on. This will turn on the transistor T₂₄ at the nextstage and turn off the transistors T₂₅ and T₂₆, so that a retardignition signal is provided on the line l₂.

The switch circuit functions to delay the ignition timing when theengine starts (in this case, the starter is driven to drop the powervoltage under 9 volts), and after the engine runs for warming-up (thetemperature of the cooling water goes beyond 50° C.). Under one of thefollowing conditions it will be required to run the engine by a retardignition timing.

(1) When the engine decelerates.

(2) When the engine is in the idling mode.

(3) When the engine operates under a heavy load at a lower speed.

(4) When the engine starts.

(5) When the engine is driven on a heights.

The employment of the retard ignition timing is to reduce nitrogenoxides (NO_(x)) in the exhausted gas for (1) to (3), is to improve thestart characteristic of the engine for (4), and is to compensate forexcessively advanced ignition timing for (5). Therefore, it is possibleto design various switch circuits by combining the above conditions.

A resistor 70 is connected to the positive line of the battery betweenthe amplifier circuit 2 and the ignition circuit 3 and acts to limit thevoltage applied to the amplifier circuit. A Zener diode 80 is connectedin paralle with the reference ignition signal generator 1 and acts tostabilize the voltage applied to the reference ignition signal generator1 and the amplifier circuit 2.

There is shown in FIG. 8 (a) an output voltage waveform from thetriangular pulse forming circuit 9, that is, the terminal voltagewaveform across the capacitor circuit Q, in which the solid lineindicates the waveform when the engine runs at a low speed and thechain-dotted line indicates the waveform when the engine runs at a highspeed with a half of the period at the above-mentioned low speed.

As has been already described earlier, when an ignition has been made,the capacitor circuit Q is charged with constant current I₂ (which isexpressed in expression (5)) through voltage V_(ref). The chargingoperation will continue until the next referenc ignition timing signalreaches. FIG. 8 (b) shows the potential on the output line l₂ from theretard ignition signal generator B, and FIG. 8 (c) shows the current onthe primary winding of the ignition coil. Where, T is the period of theignition timing and α is the width of the retard ignition signal.Accordingly, the capacitor circuit Q is charged only during the time(T-α), and is discharged during the time α to reach V_(ref). In thiscase, the voltage V_(cl) when switching is made from the charging to thedischarging is written in the form of the expression which appearsbelow. ##EQU6##

Where, C indicates the capacity of the capacitor circuit Q.

When a reference ignition signal generates, a trigger signal is issuedfrom the trigger circuit 7 to form the constant-current dischargingcircuit in the capacitor circuit Q. and thereby to discharge thecapacitor circuit Q through the above-mentioned constant current. Thedischarging continues until the terminal voltage across the capacitorcircuit Q reaches V_(ref). The voltage V_(ref) is expressed as follows.##EQU7##

Arranging expressions (6) and (7), it follows: ##EQU8##

Re-arrangement of the above expression with respect to I₁ and I₂ gives:##EQU9##

Now, suppose that the time width of the retard ignition signal is α andthe retard angle is θ.sub.α, so that, from expression (2), ##EQU10##

Which means that since N·T is a constant determined by the number ofcylinders for the engine, the retard angle θ.sub.α is determined by theratio of the charging current I₂ to the discharging current I₁,independently of the number of revolutions of the engine. In otherwords, it is of importance to bear in mind that the retard angle θ.sub.αvaries linearly with the charging current I₂. Therefore, when the switchSW in the triangular pulse forming circuit 9 is turned to the h_(o)terminal position to provide to the terminal h_(o) a control signalwhich depends on the number of revolutions or the load for the engine,the retard angle of the ignition signal can vary linearly with thecontrol signal, which allows the retard angle to be controlledappropriately.

There are shown in FIG. 9 a conventional advance angle characteristic Awhich is obtained from a centrifugal advance mechanism a negativepressure advance mechanism, and a retard ignition characteristic B whichis delayed by a constant angle with respect to the advance anglecharacteristic A, according to the present invention.

The charging current I₂ may be also changed in a step manner by means ofa circuit shown in FIG. 11. The circuit of FIG. 11 is the same as thatof the triangular pulse forming circuit 9 in FIG. 1, except that theswitch SW and the resistor 907 in FIG. 1 is replaced with other circuitelements. In FIG. 11, across the Zener diode 906, are provided resistors907c, 907b and 907a and the diode 908. A connection between theresistors 907b and 907a is connected directly to the emitter of thetransistor T₃₀, and a connection between the resistors 907b and 907c isconnected directly to the emitter of the transistor T₃₁. The collectorsof the transistors T₃₀ and T₃₁ are connected directly to the cathode ofthe Zener diode 906, and the bases thereof are connected directly to thecontrol signal generator 930.

The control generator 930 functions to apply to the bases of thetransistors T₃₀ and T₃₁ a signal to render conductive either of thetransistors T₃₀ or T₃₁ cuts off the both, according to the number ofrevolutions or the load for the engine; so that the resistor 907c or907b or the two resistors 907b and 907c out of the three resistors 907a,907b ad 907c are short-circuited, or the three resistors are activated,which allows the charging current I₂ expressed in expression (5) to bechanged stepwise.

With the arrangement as has been disclosed, the present invention hassuch as advantage that the retard ignition signal generator B isinserted in parallel with the reference ignition signal transferringline having a delay circuit to delay the transfer of the referenceignition signal so as to eliminate the possibility that the referenceignition signal activates the ignition circuit when the retard ignitionsignal generator activates, which provides a stable ignition timingcontrol characteristic.

According to the present invention, further, as long as the switch Sremains at the open position, a discharging circuit is formed and heldto discharge the capacitor in the retard ignition signal generator.Therefore, when the retard ignition signal generator is activated byturning the switch S on, first, the charging of the capacitor starts,the discharging thereof occurs after a reference ignition signal reachesthere, and then a retard ignition signal generates according to thereference ignition signal, which provides suitable control of theignition timing, without misfiring.

According to a further feature of the present invention, a suitableignition timing characteristic can be obtained with respect to thevoltage fluctuation, without variations in the retard angle.Furthermore, the embodiment disclosed herein according to the presentinvention may be arranged in a manner suitable to employ integratedcircuits. In addition, possible reduction in the capacities of the usedcapacitors can result in a compact system and low cost.

While the present invention has been explained with reference to thepreferred embodiments shown in the drawings, it should be understoodthat the invention is not limited to those embodiments limited butcovers all other possible modifications, alternatives and equivalentarrangements included in the scope of the appended claims.

What we claim is:
 1. The ignition timing control system for an internalcombustion engine comprising a circuit for generating a referenceignition signal in synchronism with the rotation of the engine, acircuit for generating a retard ignition signal at a point shifted by aselected shaft angle of the engine from the reference ignition signal,and an ignition circuit for controlling the ignition timing of theengine according to the retard ignition signal, wherein said retardignition signal generator includes a capacitor circuit for charging anddischarging, a first current circuit for always supplying a firstcurrent to the capacitor circuit, said first current circuit forming afirst current mirror circuit including a first transistor coupled tosaid capacitor circuit, a second current circuit for supplying saidcapacitor circuit with a second current which has reverse polarity tothe first current and which is equal to the sum of the first current anda discharge current from the capacitor circuit, said second currentcircuit forming a second current mirror circuit including a secondtransistor coupled to said capacitor circuit, a switching circuit whichstarts the flow of the second current in synchronism with the referenceignition signal and cuts off the second current when the terminalvoltage across said capacitor circuit reaches a reference level, and anoutput circuit for generating the retard ignition signal when theterminal voltage across said capacitor circuit reaches the referencelevel, wherein each of said first and second current circuits comprisesa series circuit of a resistor and a diode which is connected with anemitter-base path of each of said first and second transistors inparallel, so that the collector currents of said first and secondtransistors are equal to the first and second currents respectively. 2.The ignition timing control system as defined in claim 1, furthercomprising means for changing the ratio of said first current to saidsecond current according to the operation condition of the engine. 3.The ignition timing control system for an internal combustion engine asdefined in claim 2, wherein said ratio changing means includes means forgenerating a control signal according to an operation condition of theengine to control a base current of said first transistor.
 4. Theignition timing control system for an internal combustion engine asdefined in claim 2, wherein said ratio changing means includes means forgenerating a plural step control signal according to the operatingcondition of the engine to control a base current of the firsttransistor.
 5. The ignition timing control system for an internalcombustion engine as defined in claim 1 or 2, wherein said capacitorcircuit includes at least two capacitors, and the capacitors areconnected so that the total capacity of the capacitors becomes largerwhen the engine starts.
 6. The ignition timing control system for aninternal combustion engine as defined in claim 3, 4 or 2, includingmeans for decreasing a base current of said second transistor when theengine starts.
 7. The ignition timing control system for an internalcombustion engine as defined in claim 5, including means for decreasinga base current of said second transistor when the engine starts.
 8. Theignition timing control system for an internal combustion engine asdefined in claim 1, wherein said retard ignition signal generatorfurther includes a trigger circuit which generates a trigger signal insynchronism with said reference ignition signal, and means for makingsaid second transistor operative by the trigger signal to start saidsecond current.
 9. The ignition timing control system for an internalcombustion engine as defined in claim 8, wherein said trigger circuitincludes a delay circuit for delaying said reference ignition signal anda circuit for generating a trigger signal which has a pulse width of thedelay time interval of the delay circuit.
 10. The ignition timingcontrol system for an internal combustion engine as defined in claim 9,wherein said delay circuit is a Miller intergrator.
 11. An ignitiontiming control system for an internal combustion engine comprising acircuit for generating a reference ignition pulse in synchronism withthe engine, a circuit for generating a retard ignition pulse which has aleading edge in synchronism with a trailing edge of the referenceignition pulse and a trailing edge which appears at a point shifted by aselected shaft angle of the engine from the trailing edge of thereference ignition pulse, and an ignition circuit adapted to start theflow of current at a point of the leading edge of said referenceignition pulse in a primary winding of an ignition coil and to cut offthe primary winding current at a point of the trailing edge of saidretard ignition pulse, wherein said retard ignition pulse generatorincludes a capacitor circuit for charging and discharging, a firstconstant-current circuit for always supplying a first current to saidcapacitor circuit, a second constant-current circuit for supplying asecond current which has reverse polarity to and a value larger than thefirst current, a switching circuit which starts the flow of the secondcurrent in synchronism with the trailing edge of the reference ignitionpulse and cuts off the second current when the terminal voltage acrosssaid capacitor circuit reaches a reference level, and an output circuitfor generating a retard ignition pulse which has a pulse widthcorresponding to the time interval during which said second currentflows, and wherein said ignition timing control system further includesa a circuit for generating a delay pulse having a leading edge which issynchronized with the leading edge of said reference ignition pulse anda trailing edge which is delayed from the trailing edge of saidreference ignition pulse, and a circuit for applying to said ignitioncircuit an ignition pulse which has a pulse width of the time intervalfrom the leading edge of the reference ignition pulse to the trailingedge of the retard ignition pulse by combining said retard ignitionpulse with said delay pulse.
 12. The ignition timing control system foran internal combustion engine as defined in claim 11, wherein said delaypulse generating circuit is a Miller intergrator.
 13. The ignitiontiming control system for an internal combustion engine as defined inclaim 11, further including a current limiting circuit for maintainingan output current from said ignition circuit within a selected level.14. The ignition timing control system for an internal combustion engineas defined in claim 13, further including a current limit time reducingcircuit for generating an output voltage in proportion to the timeinterval during which said current limiting circuit limits the outputcurrent of said ignition circuit, wherein said reference ignition pulsegenerator includes means for controlling by said output voltage a levelfor activating a switching circuit which generates said referenceignition pulse.
 15. The ignition timing control system for an internalcombustion engine as defined in claim 11, further comprising means forcontrolling a leading edge of said ignition pulse according to a currentvalue in the primary winding of the ignition coil to obtain a requiredcurrent in said primary winding, and means for controlling a trailingedge of said ignition pulse according to the operation condition of theengine.
 16. An ignition timing control system for an internal combustionengine comprising a circuit for generating a reference ignition signalin synchronism with the engine, a circuit for generating a retardignition signal at a point shifted by a selected shaft angle from thereference ignition signal, a circuit for selecting either of saidreference ignition signal and said retard ignition signal, and anignition circuit for controlling the ignition timing of the engineaccording to the ignition signal selected by said selecting circuit,wherein said retard ignition signal generator includes a capacitorcircuit for charging and discharging, a first constant-current circuitfor always supplying a first current to the capacitor circuit, a secondconstant-current circuit for supplying to said capacitor circuit asecond current which has reverse polarity to and a value larger thansaid first current, a switching circuit which starts the flow of saidsecond current in synchronism with said reference ignition signal andcuts off said second current when the terminal voltage across saidcapacitor circuit reaches the reference level, wherein when saidreference ignition signal is selected, said selecting circuit operatesto continue the flow of said second current through said switchingcircuit.
 17. The ignition timing control system for an internalcombustion engine as defined in claim 16, wherein said retard ignitionsignal generator further includes a trigger circuit which generates atrigger signal in synchronism with said reference ignition signal,thereby to start the flow of said second current.
 18. The ignitiontiming control system for an internal combustion engine as defined inclaim 17, wherein when said reference ignition signal is selected, saidselecting circuit inhibits a trigger signal from said trigger circuit.19. The ignition timing control system for an internal combustion engineas defined in claim 18, wherein said selecting circuit further operatesto maintain continuous flow of said second current through saidswitching circuit when said selecting circuit inhibits the triggersignal from said trigger circuit.